Optical transmission apparatus

Abstract

An optical transmission apparatus includes a demultiplexing unit that demultiplexes a light input to the optical transmission apparatus into a plurality of lights; an optical attenuator that adjusts an output level of a light within a band that includes a signal light from among demultiplexed lights; a bypass unit that bypasses a light outside the band from among demultiplexed lights; a multiplexing unit that multiplexes adjusted light and the light from the bypass unit; and an optical amplifier that amplifies input light. The optical amplifier is provided at least one of a stage prior to the demultiplexing unit and a stage subsequent to the multiplexing unit.

1. An apparatus receiving a light including a wavelength division multiplexed (WDM) light in which a plurality of optical signals at different wavelengths in a waveband are multiplexed together, the apparatus comprising:
 a demultiplexer configured to demultiplex the WDM light in the light received by the apparatus into the plurality of optical signals; 
 an optical attenuator configured to adjust a level of a respective demultiplexed optical signal; 
 a multiplexer configured to multiplex together the demultiplexed plurality of optical signals after the optical attenuator attenuates the level of said respective demultiplexed optical signal, to thereby provide an adjusted, WDM light; 
 a bypass unit configured to route amplified spontaneous emission (ASE) light in the light received by the apparatus and which is outside of the waveband so that the routed ASE does not pass through the demultiplexer and the multiplexer; 
 a coupler configured to multiplex together the adjusted, WDM light provided by the multiplexer and the ASE light routed by the bypass unit; and 
 an optical amplifier having an amplification band that includes the waveband and the routed ASE light, and is provided at at least one of a stage prior to the demultiplexer so that the optical amplifier amplifies the WDM light and the ASE light in the light received by the apparatus, and a stage subsequent to the coupler so that the optical amplifier amplifies adjusted, WDM light and the ASE light multiplexed together by the coupler. 
 
   
   
     2. The apparatus according to  claim 1 , wherein the bypass unit includes a signal-band blocking filter configured to block light within the waveband so that light within the waveband is not routed by the bypass unit and then multiplexed by the coupler with the adjusted, WDM light. 
   
   
     3. The apparatus according to  claim 1 , wherein
 the bypass unit includes a transmission-factor changing unit configured to change a transmission factor of the routed ASE light. 
 
   
   
     4. The apparatus according to  claim 3 , wherein
 the transmission-factor changing unit is configured to set an upper limit for the transmission factor. 
 
   
   
     5. The apparatus according to  claim 1 , further comprising
 a drop port configured to drop an optical signal from the WDM light, wherein the drop port is positioned at a stage prior to a position at which the bypass unit routes ASE from the light received by the apparatus. 
 
   
   
     6. A method comprising:
 receiving a light including a wavelength division multiplexed (WDM) light in which a plurality of optical signals at different wavelengths in a waveband are multiplexed together; 
 demultiplexing the WDM light in the received light into the plurality of optical signals; 
 adjusting a level of a respective demultiplexed optical signal; 
 first multiplexing together the demultiplexed plurality of optical signals after said adjusting, to thereby provide an adjusted, WDM light; 
 routing amplified spontaneous emission (ASE) light in the received light and which is outside of the waveband so that the routed ASE does not pass through said demultiplexing and said first multiplexing; 
 second multiplexing together the adjusted, WDM light provided by said first multiplexing and the ASE light routed by said routing; and 
 amplifying with an amplification band that includes the waveband and the routed ASE light, said amplifying being performed at least one of a stage prior to said demultiplexing so that said amplifying amplifies the WDM light and the ASE light in the received light, and a stage subsequent to said second multiplexing so that said amplifying amplifies the adjusted, WDM light and the ASE light multiplexed together by said second multiplexing. 
 
   
   
     7. The method according to  claim 6 , wherein said routing includes blocking light within the waveband so that light within the waveband is not routed by said routing and then multiplexed by said second multiplexing with the adjusted, WDM light. 
   
   
     8. The method according to  claim 6 , wherein said routing includes changing a transmission factor of the routed ASE light. 
   
   
     9. The method according to  claim 8 , wherein an upper limit is set for the transmission factor. 
   
   
     10. The method according to  claim 6 , further comprising
 dropping an optical signal from the WDM light at a stage prior to a position at which said routing routes ASE light from the received light. 
 
   
   
     11. An apparatus receiving a light including a wavelength division multiplexed (WDM) light in which a plurality of optical signals at different wavelengths in a waveband are multiplexed together, the apparatus comprising:
 a demultiplexer configured to demultiplex the WDM light in the light received by the apparatus into the plurality of optical signals; 
 a plurality of optical attenuators configured to adjust levels of the demultiplexed plurality of optical signal, respectively, to thereby provide level adjusted optical signals; 
 a multiplexer configured to multiplex together the level adjusted optical signals, to thereby provide an adjusted, WDM light; 
 a bypass unit configured to route amplified spontaneous emission (ASE) light in the light received by the apparatus and which is outside of the waveband so that the routed ASE does not pass through the demultiplexer and the multiplexer; 
 a coupler configured to multiplex together the adjusted, WDM light provided by the multiplexer and the ASE light routed by the bypass unit; 
 a first optical amplifier having an amplification band that includes the waveband and the routed ASE light, and provided at a stage prior to the demultiplexer so that the first optical amplifier amplifies the WDM light and the ASE light in the light received by the apparatus; 
 a second optical amplifier having an amplification band that includes the waveband and the routed ASE light, and provided at a stage subsequent to the coupler so that the second optical amplifier amplifies adjusted, WDM light and the ASE light multiplexed together by the coupler; 
 a drop port positioned between the first and second optical amplifiers to drop optical signals from the WDM light in the light received by the apparatus; 
 an add port positioned between the first and second optical amplifiers to add optical signals to the WDM light in the light received by the apparatus. 
 
   
   
     12. The apparatus according to  claim 11 , wherein the bypass unit includes a transmission-factor changing unit configured to change a transmission factor of the routed ASE light. 
   
   
     13. The apparatus according to  claim 12 , wherein the transmission-factor changing unit is configured to set an upper limit for the transmission factor. 
   
   
     14. An apparatus receiving a light including a wavelength division multiplexed (WDM) light in which a plurality of optical signals at different wavelengths in a first waveband are multiplexed together, the apparatus comprising:
 a demultiplexer to demultiplex the WDM light in the light received by the apparatus into the plurality of optical signals, to thereby output a demultiplexed plurality of optical signals; 
 a multiplexer to multiplex together the demultiplexed plurality of optical signals, to thereby provide a WDM light; 
 a bypass unit to route amplified spontaneous emission (ASE) light in the light received by the apparatus and which is outside of the first waveband so that the routed ASE does not pass through the demultiplexer and the multiplexer; 
 a coupler configured to multiplex together the WDM light provided by the multiplexer and the ASE light routed by the bypass unit; and 
 an optical amplifier having an amplification waveband that includes the first waveband and the routed ASE light, and provided at least one of
 a stage prior to the demultiplexer so that the optical amplifier amplifies the WDM light and the ASE light in the light received by the apparatus, and 
 a stage subsequent to the coupler so that the optical amplifier amplifies the WDM light and the ASE light multiplexed together by the coupler.